1. Field of the Invention
This invention relates to high performance gas turbine gas generators using centrifugal compressors and radial inflow turbines, the gas generators providing a high efficiency in terms of specific fuel consumption.
2. Description of the Prior Art
There is a demonstrated need for gas turbine power plants as alternatives for diesel engines, for instance, for vehicular and other applications where a compact, lightweight engine having low specific fuel consumption (sfc) is required. Practical experience has shown that substantial space and weight savings are available using conventional gas turbines. However, the worsening of specific fuel consumption in simple cycle engines as rated power diminishes has been an accepted fact and a major drawback in prior art devices.
Prior attempts to provide gas turbine power plants have used many different configurations embodying centrifugal and radial components. For example, a known gas turbine auxiliary power unit (APU) includes a double-entry, low pressure centrifugal compressor stage and a single-entry, high pressure centrifugal compressor stage operating in series to provide compressed air both for combustion with fuel in a combustor and bleed air for external use. The hot gases from the combustor are then fed to a single stage radial inflow turbine which drives both compressors and, in addition, provides shaft power takeoff for external use in a manner consistent with a single shaft engine.
The previous inability to provide sufficient pressure ratio at acceptable component efficiencies has resulted in small power plants with low pressure ratios (i.e., less than about 12:1) with specific ic fuel consumptions substantially higher than high speed diesel engines of comparable power. In an effort to overcome these limitations, the industry has typically used one or more axial compressor stages upstream of a final centrifugal compressor stage, or two single-entry centrifugal stages, together with a conventional axial turbine for the gas generator section of the engine. For the best state-of-the-art 1000 hp gas turbine engine designs with either of these configurations, the industry currently would expect an sfc of about 0.45 at an overall pressure ratio of less than about 15:1.